1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method for processing a substrate. Examples of substrates to be processed include semiconductor wafers, substrates for liquid crystal displays, substrates for plasma displays, substrates for FEDs (field emission displays), substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photomasks, ceramic substrates, substrates for solar cells, etc.
2. Description of Related Art
In a process for manufacturing semiconductor devices, liquid crystal display devices, and the like, a cleaning process is performed to remove foreign matters from a substrate, such as a semiconductor wafer or a glass substrate for liquid crystal display devices.
For example, in a back-end-of-the-line (BEOL) process that forms a multilayer wiring structure on the front surface of a semiconductor wafer on which devices, such as transistors and capacitors, are build, a polymer removing process is performed to remove polymer residues generated by dry etching. The reason is that electric properties of the devices will deteriorate, or the yield will decrease if residues remain on the substrate.
Japanese Patent No. 5276344 discloses a substrate processing apparatus and a substrate processing method that remove particles by allowing liquid droplets of a processing liquid to collide with a substrate. In this substrate processing apparatus and this substrate processing method, a plurality of liquid droplets generated by a collision between HFE (hydrofluoroether) and nitrogen gas are allowed to collide with the front surface of the substrate while supplying pure water serving as a cover-rinsing liquid to the front surface of the substrate. A mixed liquid of pure water and IPA is mentioned as a processing liquid excluding HFE. It is considered that the reason why a low-surface-tension liquid, such as HFE or IPA, is used as a processing liquid is that smaller liquid droplets will be generated, and the number of damage occurrences will decrease if the surface tension of the processing liquid is low.
However, Japanese Patent No. 5276344 discloses generating liquid droplets of the processing liquid by use of the mixed liquid of pure water and IPA instead of HFE, but does not disclose the mixture ratio between IPA and pure water, i.e., the concentration of IPA in the mixed liquid.
If the concentration of IPA rises, a liquid droplet becomes small, and thus a shock applied to a pattern becomes small. However, a shock applied to foreign matters also becomes small. Thus, the removal rate of the foreign matters is lowered while the number of damage occurrences decreases. On the contrary, if the concentration of IPA falls, the number of damage occurrences increases while the removal rate of the foreign matters is heightened. Thus, it is difficult to optimize both the number of damage occurrences and the removal rate of the foreign matters. Particularly, an optimal processing condition for a certain substrate is not always an optimal condition for another substrate, and thus it is not easy to process a plurality of substrates under an optimal condition.